New central heating system

[news]

I need to have a new heating system installed and have begun doing some research.

There are 12 radiators which I have sized using information of the Internet and had them checked by local plumber merchants. Heating requirement for rads is 19kW. We have one family bathroom that will have a separate shower cubicle, we also have an additional shower room but that will utilise an electric shower. The property was built in

1890s and is a mid terrace has four floors (or three and a cellar) There are two rooms in the cellar one used as an office the other as a utility room.

Plumbers merchant is suggesting a 35kw boiler and having looked at various models I am leaning toward the Viessmann Vitodens 100-W condensing combi. Previously we have had Vaillant boilers and never had any trouble with them.

I am now thinking of the controls system for the installation and would appreciate some advice.

1 TVRs and a room stat? If so where is the best place for a room stat. The house is usually occupied most days as I work from home and wife works part time.

2 Should I be considering zoning?

Many thanks

[The Natural Philosopher]

First point. If you are doing the lot, why a Combi? consider normal boiler and pressurised hot water. The actual cost of say a 19KW boiler + tank may be less than 35Kw + electric shower. And you wont lose a hot shower when your wife decides to leave the sink hot tap running...

Secondly, a TVR is a hairy assed sports car. I see no need for that.

Thirdly, the luxury solution is to use thermostats and motorised zone valves everywhere to get real zone control, but its expensive and dictates that you run control wires back from each valve to control the boiler.

TRVs are not too bad, and do allow some controls, but I dont find them especially accurate, and if the main thermostat goes off, you can be left with cold rooms. Better than nothing, but pretty crap nonetheless.

BTW I have 6 bedrooms and three bathrooms plus a shower room, and only need 10KW estimated. That's the value of insulation. Consider adding some!

[geoff]

In message , news writes

Is yours terminal or are you just thinking that you should do so ?

Now is not the time of year to replace your boiler unless you need to

[Dave Plowman (News)]

The Vitodens can be configured to be weather compensated. It's a bit of a fiddle to programme it, but once done should work well.

[Andrew Gabriel]

And the smaller boiler will probably modulate down further.

Doesn't generate an efficient load for the boiler. Probably find you have demand for heat most of the time from somewhere in the house, but too little load for efficient boiler operation. If the boiler modules down to, say, 4kW minimum, then you don't want lots of zones which are each much less than 4kW output.

They work fine for most people. Have to be careful on choice of location for thermostat, and to ensure that rads in that room are not relatively oversized.

3 bedroom end-terrace 1900 house, I calculated 10.6kW. In retrospect, this seems to have been an over-estimate.

[The Natural Philosopher]

I am not so sure. If the house is brick/block it wil have a pretty high thermal time constant, and you will be runing rads wide open, so the boiler will probablly do long highish power bursts.

TRV's themselves will strangle the flow and ultimately as the house approaches the right temp., restrict water flow to just as bad, if not worse a situation.

'Work fine' is roughly equivelent to 'not too bad' in my book. However in-laws have that setup, and with a main stat in the hall, where people constantly go in and out, it leads to higher fuel bills than necessary. I think TRV's are a good answer in a smallish property that is well insulated, but with a larger and more rambling one, I think zoning is worth it, evenm if not down to a per room zone.

I actually have effectively three zones. The kitchen which is mostly Aga heted, which is fine, as thats where most action takes place, a living area with its stat and UFH, plus lower corridors and the rest is bedrooms/bathrooms, on a completely different and un master statted zone. each room has either a TRV rad or a thermo controlled hot air fan system. That whole zone is only ever used in the depths of winter - there is enough leakage from the ground floor upwards for the most part. And most of the bedrooms are not in use at any given time, and are left off.

So there are lots of ways to crack this nut: It bears thinking and discussion, and I suspect there is no optimal solution for all cases.

You need to balance

- occupancy patterns

- insulation levels in various areas

- actual house layout.

To get to a good solution.

I struggle when its sub zero and the *wind blows*. That's when we start to use wood burning stoves and open fires in the living areas and the master bedroom.

And 24x7 on the UFH.

[NT]

TRVs work fine if the rooms have similarish thermal characteristics. But if for example one side of the house is prone to overheating from solar gain and the other sees no sun, or one floor is well insulated and another not at all, you can forget about TRVs coping with the variations. They're only partially thermostatic.

Some 1890s properties are cavity walled, would be worth drilling a few test holes to see if yours is. If so, and the wall's suitable, cavity fill would offer excellent payback.

If you wanted its possible to use TRVs and a single stat, then add on afterwards heating heads to the TRVs pus a wall mounted bimetal stat. You then get proper thermostaticness and room by room zoning, plus the addons can be removed to leave a conventional system if ever sold.

NT

[Kostas Kavoussanakis]

Can you please expand on the last paragraph? What is a "heating head"; a google on 'TRV "heating head"' has been unsuccessful. I have (posted in the past) the problem that you say above, with a room that cannot be insulated as well as the others. Don't you need a motor-valve per wall-thermostat to get the boiler going? Also, I thought TRVs and wall thermostats don't mix in the same room.

I am interested if the method does not involve ripping up the floor to reach the pipes feeding the room in question.

Thanks,

-- Kostas

[The Natural Philosopher]

I think he is probably referring to something that is electrically driven and shuts the flow to a radiator.

Ive got something a bit like it on my UFH. You put current through it and a wax cylinder gets hot and expands, pushing a plunger in that shuts off the flow.

Its like a motorised valve, but smaller, quieter, and with no switch contacts. Sort of super-TRV with a remote sensor. And needing power.

[NT]

The existing system isnt modified at all, and no wires are run under floors or in walls. The idea is to add a little heating element onto each TRV so that it can be worked like a valve, electrically controlled. A bimetal stat is plugged into the nearest socket, stuck on the wall, and when the room gets hot enough the stat switches a wallwart on, which provides power to the trv head and closes the valve. You use the a/c switch contact on the stat.

You can get professional versions of this, or can make the thing yourself for little more than the cost of a basic bimetal stat. Because the cost is low, payback can be achieved, as well as better thermal control.

There should always be one rad with no TRV.

NT

[Michael Chare]

Personally I think that programmable thermostats are the best way to control a central heating system. I would locate the sensor in the main living/sitting room.

If for example you don't use the basement during the evening, I could see a case for having that on a separate zone.

[Andrew Gabriel]

If you are zoning with a view to not heating some areas for long periods, remember to allow for extra heat loss (or lack of heat gain) in the other areas to a colder area when doing your heat loss calcs. For example, if you don't do this, in this case you might struggle to heat the ground floor when you've lost the heat input from the cellar via the cellar ceiling, because you aren't currently heating the cellar.

Just something to bear in mind when zoning, if you want to be able to run just part of the house heated.

[The Natural Philosopher]

..and its a fine point as to whether inter-room insulation will lower your heat bills, or net you a massive bill for a frozen radiator..;-)

[NT]

Bear in mind a programmable stat can only deliver any benefit if you want to have different temps at different times. I cant say I found it genuinely useful myself, and havent bothered to repeat the experience. And bimetals are a lot more reliable.

NT

[The Natural Philosopher]

And can arc badly enough to totally screw TV, radio and broadband for several seconds. DAMHIKT..

[Why?]

TNP is quite right. Before I considered any of this above I would be spending my money first on looking how to insulate the house and

*then* worry about what size of boiler to use. I have the same sort of age of property in London and am considering how I can modify it without ruining it and the answer is that you cannot really! So I have decided that I will draft strip all the doors and windows really well (the Atomic Strip I put in 30 years ago is not really up to it and howls in high winds) I am considering 2.5" reduction in room size on external walls and as I put in the cornices myself will shorten and re put them on but dependent on how long you plan to live there this may or may not be a complete waste of time 12" insulation in roof void consider secondary glazing be it plastic cheap for the winter or proper permanent curtains Under floor if suspended etc etc On the heating issue I agree that use dictates if you zone or not and am inclined (as I work from home) to do this Kids have all left so top floor can be as cold as you like! Good luck Chris

[Michael Chare]

Well we have ours set to cool at night, medium during the daytime, and warmer in the evening when we are likely to be less active.

I also found that my electronic programmable thermostat achieves a much more accurate temperature control that the previous mechanical one.

[Michael Chare]

Which since it has no control is then on when the house is already warm.

We stayed in a house with this system this summer, the radiator without a TRV was the biggest one and gave out heat regardless of how warm the house was.

The only thing I could do was to set the boiler temperature lower, or switch the boiler off completely.

[Roger Chapman]

The idea behind the radiator with no TRV is that that room is controlled by the room stat and having a TRV for the room stat to fight with for control is not a good idea. Having TRVs all round and no room stat means the boiler will short cycle when the house is up to temp. Having a room stat with a full set of TRVs may have the same effect.

[Roger Chapman]

I have mine much the same although I also an early morning warm period to encourage me out of bed at a reasonable time.

There are other reasons for having a programmable stat other than continuous occupation. Different regime at weekends in particular comes to mind.

I have effectively 3 zones. Ground floor, first floor and bathroom. The bathroom radiator is on whenever the boiler is on (but has a TRV so I also have a bypass radiator).

There are periods in spring and autumn when the only time the upstairs zone calls for heat is in the early morning when it starts up before the ground floor zone. For the rest of the day there is sufficent leakage to upstairs to keep that zone up to or above temp. without any additional input.